The long term objectives of this proposal are to determine how human placental villi function normally and to dissect how placental dysfunction predisposes to intrauterine growth restriction, a condition implicated in developmental delay and neurobehavioral disorders during childhood. The Specific Aims are: (1) to determine if the sub-cellular propagation of apoptosis in human syncytiotrophoblasts is spatially transduced through adjacent regions, or via specific organelles, (2) to characterize the role of p53, Bak, and Bad in the unique pattern of apoptotic signal transmission in syncytiotrophoblasts, (3) to dissect the differences in the sub-cellular propagation of apoptosis in syncytiotrophoblasts of villi from pregnancies with intrauterine growth restriction, compared to normal controls. Intact placental function depends on syncytiotrophoblasts that provide an anatomical barrier to interface the fetal and maternal circulations. This unique syncytial epithelium regulates nutrient transport and secretion of hormones to maintain pregnancy and sustain fetal growth. Clinically relevant stressors, such as hypoxia, homocysteine, and the cytokine tumor necrosis factor-alpha, adversely affect constitutive apoptotic turnover of syncytiotrophoblasts and jeopardizes the functional integrity of the trophoblast layer. This proposal is part of our continuing effort to dissect the cellular and molecular mechanisms that underlie human trophoblast apoptosis, injury, and adaptation. We note that placental under-perfusion and exposure to toxic agents impact the occurrence and propagation of trophoblast apoptotic turnover. We use the cutting edge technologies of confocal microscopic imaging, live cell imaging techniques, and siRNA gene suppression to dissect and analyze the spatial and temporal propagation of apoptosis in vitro in cultured syncytiotrophoblasts and in villous syncytiotrophoblasts derived from in vivo specimens. We analyze the roles of key mediators, p53, Bak and Bad, in apoptotic propagation in trophoblasts. Conclusions from our research will not only shed light on normal placental function in human pregnancy but also identify mechanisms by which trophoblast dysfunction contributes to substandard fetal growth. The findings will be critical for development of new tools to identify and manage pregnancies complicated by intrauterine growth restriction.